Forecasting the volcanic ash plume of Iceland's volcano

The eruption of Iceland's volcano with the unpronounceable name, Eyjafjallajökull, has virtually ceased over the past few hours, with ash only reaching up to 6,000 feet (1800 meters), according to the latest advisory from the UK Met Office. Lightning images from UK Met Office show no new lightning strikes from the volcano's plume since midnight local time today. The relatively small amount of ash present at low altitudes will probably not be able to make it all the way to mainland Europe before falling to the surface and dissipating, since 6,000 feet is below the altitude that the strong winds of jet stream blow. Wednesday through Sunday, the volcano emitted a towering cloud of volcanic ash 6 - 11 km (20,000 - 36,000') high in the air from its 1666 meter (5500') high peak. The jet stream blows strongly at that altitude range, which allowed for efficient transport of the ash cloud to mainland Europe.

Figure 1. Lightning lights up the night sky in this photo of Eyjafjallajökull's eruption taken on April 16, 2010. Ash particles colliding together separate electric charge, much as ice particles in a thunderstorm do, leading to spectacular lightning displays. Image credit: Marco, Fulle, Stromboli Online.

Forecasts of the movement of the ash cloud are made using trajectory models, which have a number of uncertainties to consider. Firstly, the amount of ash ejected by the volcano is highly uncertain, since our measurements of this quantity are limited. Secondly, the models must compute how high the ash cloud will rise (plume rise), based on the best available measurements of atmospheric stability. Since upper air-observations are taken just twice daily by a very coarse network of balloon soundings, our knowledge of the stability is rather crude. Finally, the trajectory models use forecast winds from a global model such as the GFS model to predict where the plume may go. The forecast winds from this model do not capture much of the complicated structure of the wind field over Europe, leading to a rather fuzzy approximation of where the ash will go. Nevertheless, these models have in general done a respectable job forecasting where the ash from Eyjafjallajökull will go over the past few days.

Figure 2. Cross section of the atmosphere over time over Paliseau, France, on April 16, 2010, as observed using ground-based lidar. Image taken using a 532nm cross polarization NFOV telescope. Note how the ash layer sinks closer to the ground as time progresses, as gravity makes the ash sink to the ground. There may also be some atmospheric subsidence occurring (downward moving air due to large-scale atmospheric processes.) Image credit: Ray Hoff, World Meteorological Organization's Global Atmosphere Watch's Aerosol Lidar Network (GALION).

For the next few days, these models continue to indicate that northwest winds at the jet stream level will continue to affect Iceland. As a result, Spain, Portugal, and Greece will offer the best locations to fly from. The northwesterly winds are expected to continue for the remainder of the week, thanks to an upper-level trough of low pressure over northern Europe. On Saturday April 24, the ECMWF model predicts that the trough will slide eastwards, and a ridge of high pressure will build over Europe. This will bring upper-level winds out of the southwest to Iceland, directing any volcanic ash northwards over the North Pole. Thus for the remainder of this week, expect continued ash clouds over much of Europe if the volcano resumes significant eruptions. But by next Sunday, the ash over Europe should decline considerably. For the latest one-day forecasts of where the ash cloud is expected to go, consult the UKMET Office. The Rhenish Institute for Environmental Research at the University of Cologne also has some excellent simulations from an atmospheric dispersion model of Eyjafjallajökull's eruption plume. The Norwegian Institute for Air Research runs a computer trajectory model called FLEXPART that has 1-day forecasts showing a cross section of the atmosphere. NOAA's Air Resources Laboratory (ARL) lets you perform your own model run using their HYSPLIT model, going out up to 48 hours, using the GFS model as input.

C and S FL have been getting rain daily now and more may come this afternoon as our seabreeze fronts get active.

The mean date of the start of the rainy season across southeast florida is May 20, so we probably beginning the transition period. We got very little lightning from the activity yesterday, which means that it's still too early. I'm not sure if whatever is left of El Niño will have an impact on the start of the rainy season. Past starts in El Niño years has varied some, so no clear signal from what I can tell.

Quoting stoormfury:morningthe start of the tropical wave train in may could tell us how the season will unfold for the MDR. This all depends on how strong these waves exit the african coast and how long they mentain their identity and strengh

That is a good point. The water is so warm there we may even have a early season Cape Verde type storm.

...DISCUSSION... MEDIUM-RANGE MODELS CONTINUE TO SHIFT A LARGE UPPER SYSTEM EWD ACROSS THE CENTRAL AND ERN U.S. WITH TIME...WITH A GRADUAL WEAKENING/DEAMPLIFICATION OF THE SYSTEM PROGGED. AS THE SYSTEM BEGINS TO OPEN/WEAKEN -- PARTICULARLY FROM DAY 5 /SUN. APR. 25/ ONWARD...MODEL AGREEMENT SLOWLY DECREASES AS WELL. WHILE ENHANCED SEVERE POTENTIAL WILL LIKELY SPREAD ACROSS THE SERN U.S. UNTIL THE MAIN SURFACE FRONT MOVES OFFSHORE ON OR AROUND DAY 7 /TUE. APR. 27/...CONFIDENCE WITH RESPECT TO TIMING AND LOCATION DECREASES STEADILY INTO THE PERIOD.

ATTM...WILL MAINTAIN AN OUTLOOK AREA CENTERED INVOF THE MID AND LOWER MS AND TN VALLEYS DAY 4 /SAT. APR. 24/...AS A STRONGER SHORT-WAVE TROUGH EMBEDDED WITHIN THE CYCLONIC FLOW AROUND THE MAIN UPPER LOW IS PROGGED TO SHIFT ACROSS THIS REGION. WITH STRONG DEEP-LAYER WIND FIELD AND MOIST/LIKELY UNSTABLE AIRMASS IN PLACE AHEAD OF THIS FEATURE AND ASSOCIATED SURFACE FRONT...WIDESPREAD SEVERE WEATHER APPEARS LIKELY.

AGAIN -- WHILE AT LEAST SOME SEVERE THREAT SHOULD SHIFT STEADILY EWD WITH TIME DAYS 5-6-7...MODEL DIFFERENCES PRECLUDE HIGHLIGHTING SPECIFIC THREAT AREAS BEYOND DAY 4.

morningthe start of the tropical wave train in may could tell us how the season will unfold for the MDR. This all depends on how strong these waves exit the african coast and how long they mentain their identity and strengh

Tropical Cyclone Warning Center PerthTROPICAL CYCLONE OUTLOOKForecast for area south of 10S between 90E-125E2:00 PM WST April 21 2009=====================================

There is a developing low in the monsoon trough south of Indonesia near 10S 117E. This low is expected to develop into a tropical cyclone late on Thursday or on Friday as it moves to the southwest. It is not expected to affect Christmas or Cocos Islands or the Australian mainland.

Quoting pottery:Greetings.Another hot one here today, peaked at 96.8f at the airport (no, the guage is not on the paved runway).But the showers over the past few days seem to have put out the fires. Nice clear night right now.